 pancreatic enzymatic secretions occur in three phases the thawed smell taste of food causes pancreatic stimulation by a vagus nerve this is known as cephalic phase vagus nerve releases acetylcholine which acts on SNR cells as well as on dubbed cells when food is in stomach gastric distention stimulates vagovagal reflexes where afferents of vagus are stimulated by gastric distention and efferents of vagus stimulate pancreatic secretion this is gastric phase but these two phases do not contribute much to pancreatic secretion when chyne enters the diodenum the contents of the chyne especially fats and peptides stimulate eye cells of diodenum which release cck in blood chyne also the ph content of the chyne causes stimulation of S cells of diodenum which releases secretin into blood cck is the major stimulator of enzymatic secretion of pancreas while secretin is major stimulator of bicarbonate and water secretion from duct cells of pancreas secretin acts on duct cells and increases the conductance of this chloride channel because only when chloride is available in lumen can bicarbonate be secreted by bicarbonate chloride exchanger in a disease known as cystic fibrosis mutations of this channel occur and there is decrease in watery and bicarbonate secretion from the pancreatic gland even though cck is major stimulator of pancreatic enzyme secretion and secretin a major stimulator of bicarbonate secretion both also help each other by increasing each other's function